Analogous channel method for performance monitoring and equalization in optical networks

Abstract

Performance monitoring and equalization of DWDM optical links equipped with optical add/drop multiplexers (OADMs) at one or more sites is effected by selecting a direction of transmission and the end sites from the point of view of equalization.Performance monitoring and equalization of DWDM optical links equipped with optical add/drop multiplexers (OADM) is presented in this application. This approach in involves conceptually converting a multiple ends system to a "two-end" system with analogous channels (AC) to simplify the network management and equalize the DWDM channel performance. All analogous channels are treated as originating at a source analogous end and terminating at a destination analogous end for the purpose of equalization. The input power for all ACs, is adjusted at the source AE to obtain equal channel performance at the destination AE.

We claim:  
     
       1. A method for performance monitoring and equalization of an optical link between two line terminating equipment (LTE/REGEN) sites of an optical network and being provided with at least one intermediate sites equipped with an optical add/drop multiplexers (OADM), comprising: 
       selecting a direction of transmission and accordingly defining one of said LTE/REGEN sites as a source analogous end (AE) and the other as a destination AE;  
       converting said optical link into a two-ended analogous system of J analogous channels (AC), each AC(j) originating at said source AE and terminating at said destination AE; and  
       adjusting the input power of each AC(j) to obtain a substantially equal performance parameter for all ACs, where J>2, j is the identifier of an AC, and jε[1,J].  
     
     
       2. A method as claimed in  claim 1 , wherein performance parameter is the BER margin. 
     
     
       3. A method as claimed in  claim 2 , wherein said step of adjusting the input power comprises: 
       for each AC(j), setting an initial input power Pini_j at said transmitter and measuring the optical signal-to-noise ratio OSNR_j at said receiver;  
       determining a distance to failure D_j;  
       determining the minimum and the maximum distances to failure among said distances to failure calculated for each AC(j) and calculating the difference ΔD between the maximum and the minimum distances to failure;  
       whenever said difference ΔD is less than a second threshold, adjusting said initial input power Pini_j; and  
       repeating steps (b) to (d) unit said difference becomes greater or equal to said second threshold.  
     
     
       4. A method as claimed in  claim 3 , further comprising the step of adjusting the power at the input of said receiver according to a provisioned value; whenever said difference is greater than said second threshold. 
     
     
       5. A method as claimed in  claim 3 , wherein said step (a) of setting an initial input power Pini_j comprises: 
       providing a total target input power Pin_tot_target at said source AE;  
       calculating said initial input power and setting the power of said transmitter to said initial input power Pini_j;  
       measuring a channel failure indicator indicative of said AC(j) failure; and  
       whenever said channel failure indicator show that said AC(j) is failed, effecting one of adjusting said initial input power of said AC(j) and adjusting said initial input power for all other channels of said optical link by a same amount until said channel failure indicator shows that said AC(j) is not failed.  
     
     
       6. A method as claimed in  claim 5 , wherein said channel failure indicator is one of the BER value and rate R. 
     
     
       7. A method as claimed in  claim 3 , wherein said step (b) of determining a distance to failure comprises: 
       setting a fail value for said channel failure indicator;  
       setting the power of said receiver at a specified value Prx_j;  
       measuring said channel failure indicator for said specified value Prx_j and comparing same with said fail value;  
       adjusting said initial input power Pini_j until said channel failure indicator attains said fail value, and recording said input power as an attenuated power Patt_j;  
       re-setting said initial input power Pini_j at the input of said transmitter; and  
       calculating said distance to failure as the difference between said initial input power and said attenuated power.  
     
     
       8. A method as claimed in  claim 7 , wherein said channel failure indicator is one of the BER value and rate R. 
     
     
       9. A method as claimed in  claim 8 , wherein said new input power P_j is calculated according to equation P_j=Pini_j−Coeff*(D_j−D_min), where Coeff is an adjustment coefficient. 
     
     
       10. A method as claimed in  claim 3 , wherein said step (d) of adjusting said initial input power Pini_j comprises: 
       calculating a new input power Pi_j for each AC(j) based on said initial input power Pini_j and said distance to failure; and  
       re-setting said input power at said transmitter to said new input power P_j.  
     
     
       11. A method as claimed in  claim 1 , wherein said step of converting comprises, for each communication channel (j) originating and terminating at and between said LTE/REGEN sites: 
       identifying a transmitter and a receiver connected by said communication channel;  
       if said transmitter is physically located at an intermediate site, converting said channel into an add AC having said transmitter located at said source AE, and a lossless fiber span between said intermediate site and said source AE;  
       if said receiver is physically located at an intermediate site, converting said channel into a drop AC having said receiver at said destination AE, and a lossless fiber between said intermediate site and said destination AE; and  
       converting said channel into an express AC when said transmitter and said receiver are physically located at respective LTE/REGEN sites.